German utility model registration G 84 26 813.1 discloses a linear drive wherein the conversion of a rotational movement into a linear movement is made with toothed belts. A form-tight meshing engagement is generated by the tooth profile between toothed belt and linear toothed counterpiece whereby a transfer of the rotational movement into a linear movement of the toothed counterpiece is possible. The toothed counterpiece is usually configured as a rack made of steel or the like. Generally, the rack is configured to have a specific length. According to utility model registration G 84 26 813.1, it is also conceivable to use individual rack segments which are separated from each other by gaps.
The toothed belt is usually made of elastomeric material and is, for example, driven by a pinion and is brought into engagement with the toothed counterpiece via direction-changing rollers. With the aid of additionally mounted hold-down rollers, it is ensured that an adequate number of teeth remain in engagement with the toothed counterpiece between the entering end and the exiting end of the toothed belt. The toothed belt is pretensioned by adjusting the direction-changing rollers in that the mutual spacing of the direction-changing rollers is increased.
The known linear drives include a toothed belt having a standard tooth profile which engages in a correspondingly profiled toothed counterpiece of the same pitch.
For force transmission, the toothed belt engages over a predetermined length (the so-called engagement length) in the toothed counterpiece from the entering end up to the exiting end. The force transmission to the toothed counterpiece takes place with a specific thrust force which is proportional to the tooth load.
The toothed belt itself has a specific stiffness which is dependent upon the stiffness of the tension reinforcement (that is, the so-called cord), the cord spacing as well as the width of the toothed belt. The tension reinforcement is disposed in the toothed belt.
A disadvantage of the known linear drives is that a thrust force, which is too high, leads to increased tooth loading. Additionally, the known linear drives have the disadvantage that very large forces occur at the exiting end of the toothed belt, that is, on the pull end at the end of the engagement length. These forces lead to a premature wear of the toothed belt and therefore of the linear drive. Often, disturbing running noises occur.